(1) Field of the Invention
The present invention relates to a sealing compound for cans. More particularly, the present invention relates to a sealing compound for cans, which can effectively prevent rusting on the metal-exposed surface of the cut edge of a can end member.
(2) Description of the Prior Art
In the conventional process for the manufacture of cans, as shown in FIG. 1, a liquid sealing composition called "sealing compound" is lined in an annular groove 2 of a can end member (can lid) 1, and a sealing compound layer (gasket) 3 is thus formed, if necessary, by drying. Then, the can end member 1 is double-seamed to a flange of a can body 5, as shown in FIG. 2, to form a can. This sealing compound comprises as the main ingredient an aqueous latex of a styrene-butadiene rubber (SBR), and a composition formed by adding a tackifier, a filler, an emulsifier or a dispersant, a thickening agent and the like to this aqueous latex is ordinarily used for the manufacture of cans.
It has been found that when this known aqueous sealing compound is used, rusting often takes place on the cut edge 4 of the can end member 1. Since a surface-treated steel plate such as a tin-plated steel plate (tinplate) or a chromic acid electrolytically treated steel plate (tin-free steel plate) is used as the can end member, occurrence of rusting on the surface to which the sealing compound is directly applied is prevented because of the presence of the covering layer, but in the above-mentioned cut edge 4, the steel substrate is exposed and the aqueous sealing compound adheres to this steel-exposed portion to cause rusting. If rusting takes place on the cut edge 4 of the can end member 1, when the can end member 1 is double-seamed to a can body filled with the content, rusts are separated and incorporated into the content to degrade the flavor and taste of the content, and furthermore, filiform corrosions are formed on the double-seamed portion to impair the appearance of the can.